1. Field of the Invention
The present invention relates generally to frequency divider circuits and, more particularly, to an improved CMOS frequency divider circuit.
2. Prior Art Statement
Frequency divider circuits have been well known and widely used in the various semiconductor technologies for many years. However, only relatively recently has the complementary-metal-oxide-semiconductor (CMOS) technology become sufficiently well understood to make large scale integration (LSI) economically feasible. Such advances have made possible frequency divider circuit implementations which would be unavailable in other technologies. In "CMOS: Higher speeds, more drive and analog capability expand its horizon" (Bingham, Electronic Design 23, Nov. 8, 1979, Pp. 74-82), a static divide-by-3 requiring 24 transistors is shown in FIG. 2b. Using the inherent capabilities of CMOS, however, a dynamic divide-by-3 circuit requiring only 12 transistors can be fabricated as shown in FIG. 2a (see also FIG. 1 herein). However, the latter circuit may, in some circumstances, assume forbidden states from which exit to a valid state is impossible.